Ultrastructural examination of Gibberella fujikuroi mycelia: effect of immobilization in calcium alginate beads

Abstract

Ultrastructural examination of free and calcium alginate immobilized Gibberella fujikuroi mycelia showed that in addition to the changes occurring during the transition phase from primary to secondary metabolism, there are several alterations in the ultrastructure of hyphae as a response to microenvironmental changes owing to immobilization constraints. Internal changes included (i) the presence of large glyoxisomelike bodies and of active vesicle-generating systems, which appeared as cloudy structures in electron micrographs; (ii) the formation of endocells, resulting in hyphae with up to three cell walls and the concomitant accumulation of secondary metabolites, mainly pigments, in peripheral cell compartments; and (iii) the progressive development of autophagic vacuoles involved in the turnover of cell constituents.Key words: Gibberella fujikuroi, immobilized fungi, alginate entrapment, ultrastructure modification, immobilization.